Relationship Between Ethylene And Flavonoid Synthesis And Functional Analysis Of Wheat Anthocyanin Glycosyltransferase

Flavonoids are one of the most important secondary metabolites in plants.They have six major categories such as anthocyanins.As a kind of antioxidants,flavonoids not only play important functions in plants,but also have important health and medicinal values,e.g.the accumulation of anthocyanins in mature fruits enhances nutrition.Ethylene is an important gas hormone in plants.It plays key roles in plant growth and development,especially in the process of photomorphogenesis and fruit ripening,both of which follows by anthocyanin accumulation.The studies concerning the relationship between flavonoids and ethylene mostly focused on the mature stage rather than postgermination stage.On the other hand,flavonoids are often glycosylated,and the glycosylation affects the roles of flavonoids in stress response,which is seldomly studied in wheat.In this paper,based on the two questions,we conducted the following studies.Under the treatment of ACC,the precursor of ethylene synthesis,hypotocyl and cotyledon petiole became bright,anthocyanin content was reduced,and the expression of DFR and ANS,encoding the enzymes catalyzing the synthesis of anthocyanins was decreased;while the treatment of AgNO3,the inhibitor of ethylene receptor,had the opposite effect.The mutation of ethylene receptor and EIN3,the key modulator of ethylene signaling pathway both mimicked the effect of AgNO3 treatment.EIN3 can bind to the promoter of CHS and DFR.The results indicate that ethylene restricted the synthesis of flavonoids at postgermination stage possibly via directly modulating the synthesis of flavonoids.The mutation of CHS,the key enzyme involved in the flavonoid synthesis pathway,attenuated the phenotype of the ethylene treatment:inhibition of hypotocyl elongation and cotyledon opening,indicating flavonoids are involved in the reponse to ethylene at postgermination stage.The mutation of anthocyanin and flavonol synthesis branches had no such effect,suggesting other flavonoids may participate in the process.In comparison to the wildtype,chs mutant accumulated more ROS in hypotocyl,and was insensitive to ethylene regarding the ROS level.We isolated a wheat anthocyanin glycosyltransferase TaUGT.The expression of the gene was reduced upon abiotic stress,and its encoding product localized in ER,Golgi apparatus,and nucleus.TaUGT had no in vitro activity catalyzing glycosylation of anthocyanins.TaUGT ecotopic expression in Arabidopsis reduced the tolerance to MV and PEG,primarily indicating that TaUGT plays negative role in abiotic stress tolerance.